The display device is provided with an input device (touch sensor or touch panel) for inputting information through touching operation (contact pressing operation, which will be simply referred to as touching hereinafter) by means of a user's finger or a pen, and used for the mobile electronic device such as a PDA and a mobile terminal, various types of electric appliances, automated teller machines, and the like. There has been introduced a well known touch panel of resistance film type as described above, which detects change in the resistance value of the touched portion, the touch panel of capacitance type which detects change in the capacitance, and the touch panel of optical sensor type which detects change in light quantity.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-511799 discloses the touch panel of capacitance type. The disclosed touch panel includes longitudinally arranged electrodes (X-electrodes) for detection and horizontally arranged electrodes (Y-electrodes) for detection, which are two-dimensionally matrix arranged in longitudinal and horizontal directions so that each electrode capacitance is detected by the input processing unit. When the touch panel surface is touched with a conductor, for example, a finger, each electrode capacitance is increased. The input processing unit then detects increase in the capacitance so that an input coordinate is calculated based on a signal of detected capacitance change of each electrode.
As disclosed in Japanese Unexamined Patent Application Publication No. 2003-511799, the touch panel of capacitance type is configured to detect the input coordinate by detecting each capacitance change of the respective electrodes for detection on condition that the conductive article is used as the input element. When the touch panel of capacitance type is touched with a nonconductive material such as a resin stylus used for the resistance film type, the capacitance of the electrode hardly changes, thus failing to detect the input coordinate.
Japanese Unexamined Patent Publication No. 8-179871 discloses a combination of touch panel and transparent digitizer as the input device which serves as the touch panel and the digitizer so as to allow touching operation of both the finger and the input pen.
The device disclosed in Japanese Unexamined Patent Publication No. 8-179871 is capable of distinguishing between the touch with the finger and the touch with the pen. The aforementioned device needs more cost and has a complicated structure, which requires use of the dedicated pen for the digitizer as the input pen since the generally employed resin pen and the metal pen are unavailable for the inputting operation.
Meanwhile, the inventors found the difference in the property of the signal to be detected between the case where the touch panel of capacitance type is touched with the finger or the conductive pen, and the case where it is touched with the insulating pen.